The goal of this research program is to understand the role of early experience in changing the subsequent responses of the mammalian brain to environmental stimuli. The research is focused on our finding that early experience by Norway rat young with a particular odor not only induces a behavioral prefernce for that odor, but induces an enhanced response in the olfactory system of the young to that same odor. The pups normally develop an attraction to the odor of their mother during early life, allowing the young to maintain contact with their parent during a time in their lives when they are mobile enough to leave the maternal nest. The enhanced olfactory bulb response has been observed with the use of a technique that allows a comparison of the differential uptake of 14C 2-deoxyglucose, a glucose analogue that remains in the neurons in an incompletely metabolized state. This measure reflects what is most probably differential neural activity. We will first define the conditions under which the potentiated response occurs and then examine several possibilities for the structural changes underlying this phenomenon.